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From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Thu, 22 Nov 2018 08:50:47 -0800
Message-ID: <CAHk-=wh=_T=A53+o4zLNbKio43LGqVDb0KCbWPDvAg54bRDmWw@mail.gmail.com>
Subject: Re: remove the ->mapping_error method from dma_map_ops V2
To:     Christoph Hellwig <hch@lst.de>
Cc:     iommu@lists.linux-foundation.org, jdmason@kudzu.us,
        joro@8bytes.org, David Woodhouse <dwmw2@infradead.org>,
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        "the arch/x86 maintainers" <x86@kernel.org>,
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On Thu, Nov 22, 2018 at 6:03 AM Christoph Hellwig <hch@lst.de> wrote:
>
> The 0 return doesn't work for direct mappings that have ram at address
> zero and a lot of IOMMUs that start allocating bus space from address
> zero, so we can't consolidate on that, but I think we can move everyone
> to all-Fs, which the patch here does.

Hmm. Maybe not limit it to just all ones, but actually use the
(standard, for the kernel) IS_ERR_VALUE()?

That basically reserves the last 4095 values in an unsigned long for
error values.

Then those functions could actually return *what* error they
encountered, using just plain

        return -ENOMEM;

or whatever?

               Linus